I don't think she still loves her stepdad. Like Fuyuki said, Kisaki doesn't need her "help" anymore—pretty much indicating that she's already moved on.
Actually, I think when Eri asks Kisaki, "But you love Fuyuki, right?" and Kisaki replies "Of course," that's Kisaki revealing her true feelings.
But she still helps Eri because she knows Fuyuki's happiness lies with Eri. Kisaki used to believe that if the person she loved didn't love her back, then that person might as well die. But she's changed.
When she heard Fuyuki's thought that she'd rather suffer if it meant making the person she loves smile again—that really changed Kisaki. Now, Kisaki wishes for their happiness, even if it means she'll suffer for the one she loves.
Because, as she said: "Fuyuki said I was kind. Because of that, I feel like I can became kinder." to wishes them happiness.
Going back and re-reading it again, I agree with you.
At first I thought it was Kisaki just saying she was no longer in pain over her feelings for her stepfather - given her whole relationship with Fuyuki was mutual painful unrequited love. So at minimum I figure she'd reckoned with her feelings and had come to a healthy position over them, but I thought it was still ambiguous as to whether she loved him.
But I think it's at best a difference without a distinction, because the operative bit is she's no longer hurting. But also I don't see how any romantic feelings
could persist that wouldn't be painful for her given the exact situation, so it arguably makes the most sense that she's moved past them.
I'm still up in the air on whether she has romantic feelings for Fuyuki, though it would make sense that she would even if their relationship was "pretend" and built upon mutual need and pain--just by virtue of their time and proximity with one another. The exact term Eri uses is "like", but....it's Eri, so I think that exact word usage is significant but also purposefully ambiguous given its source.
I absolutely will say Kisaki considers Fuyuki extremely important to her, but what precise form of "love" or "like" her feelings take, I'm reading as being left up to the reader to decide.
She clearly cares enough about Fuyuki to quash any hypothetical romantic feelings though, given Fuyuki's heart is fully set on Eri, and again it's kind of a moot point because their relationship together will end as it has been up to this point with both of their unrequited love arcs either having resolved, or being imminently resolved (one way or the other).
